Alternaria diseases of potatoes: epidemiology and management in Israel

D. Shtienberg

Department of Plant Pathology and Weed Research, ARO, the Volcani Center, Israel

Potato production in Israel

Cultivated area ~16,000 ha

Egypt

Jordan

Lebanon

Syria

Elat

Beer-Sheva

Tel-Aviv

Jerusalem

Haifa

Nazareth

25 km.

N

~500 ha in the north

~3,000 ha in the Sharon area

~12,300 ha in the northern Negev

~200 ha in the Arava

temperature

radiation

Tem

pera

ture

(oC

)

So

lar

rad

iati

on

(µ

E/m

2/m

in)

10

20

30

40

0

1000

2000

3000

Month of the year

VI X II VI

Autumn Spring

Potatoes are produced in Israel in two

growing seasons

Late blight – Phytophthora infestans

Early blight – Alternaria solani

Necrotic lesions – Alternaria alternata

Observations – early blight

1. The primary factor governing early blight intensity

is host physiology, as affected by the

environment;

2. The disease is intensified in senescing leaves

towards the end of the growing season.

pathogen

environment

host

disease

host

Vegetative stage

Conceptual model describing the changes in host response to early blight over time

tuberization

Ho

st

resp

on

se

Resist.

Sus.

emergence harvest

Using the conceptual model for describing differences among the two growing seasons

tuberization

Ho

st

resp

on

se

Resist.

Sus.

emergence harvest

From: Shtienberg et al. (1996) Plant Disease 80:994-998

Autumn season D

ise

as

e +

se

ne

sc

en

ce

severi

ty (

%) Spring season

Dis

ea

se

+ s

en

es

ce

nc

e

se

ve

rity

(%

)

Using the conceptual model for describing the response of cvs. with different maturity levels

tuberization

Ho

st

resp

on

se

Resist.

Sus.

emergence harvest

tuberization

Ho

st

resp

on

se

Resist.

Sus.

emergence harvest

Using the conceptual model for describing the response of cvs. with different genotype

resistance levels

No need to spray “supplementary” sprays

Using the conceptual model for describing the need for fungicide application

tuberization

Ho

st

resp

on

se

Resist.

Sus.

emergence harvest

Integrated management strategy for EB + LB

Components in the strategy

•the growing season (autumn or spring)

•genotype resistance (to EB and to LB)

•age related resistance (to EB)

•weather suitability (to EB and LB)

•fungicide type and efficacy

The goal: to effectively manage both diseases

emergence

Systemic against EB

Full rate protectant

Sprays against EB

Autumn season: management of EB

Host sus. to EB

No need to

spray

“supplementary” sprays

tuberization

Ho

st r

esp

on

se Resist.

Sus.

emergence harvest

emergence

Systemic against EB

Full rate protectant

Sprays against EB

Half rate protectant

A. no report of LB in the region

and LB Autumn season: management of EB

Host sus. to EB

emergence

Host sus. to EB

Systemic against EB

Full rate protectant

Sprays against EB

Half rate protectant

B. LB in the region but not in the field

and LB Autumn season: management of EB

LB in the region

Sprays against LB

emergence

Host sus. to EB

Systemic against EB

Full rate protectant

Sprays against EB

Half rate protectant

and LB Autumn season: management of EB

LB in the region

Sprays against LB

LB in the field

Systemic against LB

C. LB in the region and then in the field

0

1000

2000

3000

4000

1 5

Dis

ease

+ s

en

escen

ce

severi

ty (

AU

DP

C)

a

d

9

emergence

Host sus. to EB

Systemic against EB

Full rate protectant

Sprays against EB

Half rate protectant

Autumn

season

1997/8

LB in the region

Sprays against LB

LB in the field

Systemic against LB

2

b

9

c

4

5

3

bc

7

emergence

Systemic against EB

Full rate protectant Half rate protectant

Spring season: management of LB

Systemic against LB

emergence

Systemic against EB

Full rate protectant Half rate protectant

Spring season: management of LB

Systemic against LB

LB in the region

Sprays against LB

LB in the field

emergence

Systemic against EB

Full rate protectant Half rate protectant

Spring season: management of LB

Systemic against LB

Sprays against LB

LB in the field

LB in the region

0

250

500

750

1000

1250

1 5

Dis

ease

+ s

en

escen

ce

severi

ty (

AU

DP

C)

b

a

10

emergence

Systemic against EB

Full rate protectant Half rate protectant

LB in the field

Systemic against LB

LB in the region

Sprays against LB

Spring

season

1996

2

b

10

4

a

3

3

b

5

Necrotic lesions – Alternaria alternata

Observations

1. Necrotic lesions appear suddenly in large areas,

often after heavy rain events;

2.The phenomenon is more common in crops

growing in sandy soils;

3. Alternaria alternata was isolated from necrotic

lesions and the Koch postulates were completed

and proved the pathogenicity of that fungus.

Working hypothesis

1. Heavy rains wash the nitrogen fertilizer from the

root zone.

2. Necrotic lesions appear in plants suffering from

stress imposed by sudden reduction in nitrogen

content in the foliage.

pathogen

environment

host

disease

host

0

10

20

30

0 50 100 150 200 250

N - fertigation (kg/ha)

Nec

roti

c l

es

ion

se

ve

rity

(%

)

The interactive effects of N fertigation

on necrotic lesion severity

0

10

20

30

0 50 100 150 200 250

N - fertigation (kg/ha)

Nec

roti

c l

es

ion

se

ve

rity

(%

) No. of “rain” events

0

1. 33 DAP

1. 45 DAP

2. 33 and 45 DAP

The interactive effects of N fertigation and “rain”

on necrotic lesion severity

“rain” was mimicked by over head irrigation of 600 m3 water /ha

0

10

20

30

0 500 1000 1500 2000

N concentration in leaf petioles (ppm)

Ne

cro

tic

le

sio

n

se

ve

rity

(%

)

-6

-4

-2

0

0 500 1000 1500 2000

Y = -0.0018X – 1.6

r2 = 0.784; P < 0.01 Ne

cro

tic le

sio

n

se

ve

rity

(lo

git

)

Relationships between N concentration in leaf petioles and severity of necrotic lesions

0

10

20

30

40

- Rain

- N

Fungicide a

ab

b

The interactive effects of “rain”, supplemental N

fertigation, and fungicides, on necrotic lesion

Rain and supplemental N-fertigation

+ Rain*

- N

+ Rain

+ N**

Nec

roti

c l

es

ion

se

ve

rity

(%

) No

Yes*

* 4 tebuconazole sprays **180 kg N / ha *800 m3 water / ha

Take home messages 1. Early blight development is governed by host

physiology. Its management should relate to the

response of the host to the pathogen.

2. Early blight should be managed only in the

autumn season; Late blight - in both seasons.

3.Necrotic lesions develop primarily in nitrogen-

stressed plants. Applying supplemental N

fertilization reduces necrotic lesion severity.

4. Concepts for managing potato early and late blight

were developed, examined and found effective. The

concepts are implemented commercially by Israeli

growers for more than a decade.

Thank you for your attention